Exoplanet Gliese 12b

Earth Twin or Evil Twin

Maunakea, Hawaiʻi – The discovery of a planet similar in size to Venus that’s orbiting a star in the neighborhood of our solar system raises hopes that astronomers may someday unlock the secret to why life appeared on Earth.

An international team of scientists led by the Astrobiology Center (ABC) in Japan, the University of Tokyo, the National Astronomical Observatory of Japan, and Tokyo Institute of Technology found and characterized the planet, called Gliese 12 b, based on data from NASA’s TESS space telescope, MuSCAT2 and MuSCAT3 cameras, and three Maunakea Observatories on Hawaiʻi Island: Subaru Telescope, Gemini Observatory, a Program of NSFʻs NOIRLab, and W. M. Keck Observatory.

The planet’s characteristics point to the possibility that the newly-discovered planet may have retained a certain amount of atmosphere, which makes it one of the most suitable targets out of all of the planets discovered thus far to investigate the atmosphere of a Venus-like planet.

The research is published in The Astrophysical Journal Letters.

The study of life in the universe is difficult because we have only one example of a planet where life has been confirmed: Earth. It is difficult to say which characteristics of Earth are required for life to appear, and which are irrelevant. Until we find an “Earth twin” where the conditions for life also appeared, the best astronomers can do is study “evil twins”- planets with initial conditions similar to Earth that turned out very differently, with environments unsuitable for life.

In our solar system, Venus and Mars provide two examples of lifeless “evil twins.” But with only two examples, there is still much uncertainty about how stringent or lax the conditions for life may be. Since the 1990s, more than 5,500 planets orbiting around stars other than the Sun have been discovered. However, most of these planets are hundreds of light years away from Earth, making it challenging to study them in detail.

Gliese 12 b, on the other hand, is close to our solar system, located only 40 light-years away. This makes Gliese 12b an ideal target to study with the James Web Space Telescope (JWST) and next generation ground-based telescopes.

“Follow-up observations with JWST and future ground-based observations with 30-meter class telescopes for transit spectroscopy are expected to determine whether Gliese 12 b has an atmosphere and whether the atmosphere contains molecular components associated with life such as water vapor, oxygen, and carbon dioxide,” says Masayuki Kuzuhara, a project assistant professor of ABC and lead author of the study. 

Although Venus currently does not retain liquid water on the surface, it might have in the past. Likewise, it cannot be fully ruled out that liquid water is present on Gliese 12 b’s surface.

Data from Subaru Telescope’s infrared spectrograph (IRD), Keck Observatory’s second generation Near-Infrared Camera (NIRC2) and Gemini North telescope archive data played an important role in confirming that Gliese 12 b is in fact a planet; the data ruled out a false positive scenario in which the object Kuzuharaʻs team detected might be a companion star thatʻs part of a binary system where two stars revolve around each other. 

Furthermore, the team determined that Gliese 12 b is so close to its host star, an M-class red dwarf, that one year on the planet – the time it takes to complete one orbit – lasts only 12.8 Earth days. Its radius is only 4 percent smaller than Earth’s radius, and is less than 3.9 times the mass of our planet. Gliese 12 b receives 1.6 times more radiation from its host star than Earth receives from the Sun. For comparison, Venus receives 1.9 times more radiation than Earth.

Based on this data, the team believes that Gliese 12 b is an “evil twin,” more like Venus than like Earth. But they cannot rule out the possibility that Gliese 12 b is an “Earth twin” with liquid water on its surface. Further observations will determine if Gliese 12 b is an “evil twin” or an “Earth twin.” In either case, studying Gliese 12 b in finer detail will give a better idea of the prerequisites for a life-friendly environment to develop on a planet.


The Near-Infrared Camera, second generation (NIRC2) works in combination with the Keck II adaptive optics system to obtain very sharp images at near-infrared wavelengths, achieving spatial resolutions comparable to or better than those achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is probably best known for helping to provide definitive proof of a central massive black hole at the center of our galaxy. Astronomers also use NIRC2 to map surface features of solar system bodies, detect planets orbiting other stars, and study detailed morphology of distant galaxies.


The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.


The Maunakea Observatories are a collaborative of independent institutions with telescopes located on Maunakea on the island of Hawaiʻi. Together, the Observatories make Maunakea the most scientifically productive site for astronomy world-wide. The Maunakea Observatories include: Canada-France-Hawaii Telescope, international Gemini Observatory, a Program of NSFʻs NOIRLab, James Clerk Maxwell Telescope (EAO), NASA Infrared Telescope Facility, Subaru Telescope, Submillimeter Array, UKIRT Observatory, University of Hawai’i Hilo Educational Telescope, University of Hawai‘i 2.2 Meter Telescope, Very Long Baseline Array, and W. M. Keck Observatory (Keck I and Keck II)